This is a request for an Independent Scientist Award. This grant aims to add to our understanding of the neural basis of sexually dimorphic brain function by focusing on a sexually dimorphic system that has been implicated in parental and other sexually dimorphic behaviors and functions. The hypothesis driving this grant is that sex differences in the brain not only serve to generate sex differences in centrally regulated processes and behaviors, but also may enable males and females to show remarkably similar behaviors even though their physiological and hormonal conditions differ dramatically. It does this by studying the role of the sexually dimorphic vasopressin-immunoreactive projections of the bed nucleus of the stria terminalis and the medical amygdaloid nucleus in parental behavior. The strategy is to compare two species of voles: prairie voles (Microtus pennsylvanicus), a monogamous species in which both males and females provide parental care, and meadow voles (Microtus pennsylvanicus), a promiscuous species in which only females provide parental care. This strategy allows comparison of the AvP-ir projections not only between males and females but also between males that show different parental involvement. The research will entail psychopharmacological, hormonal and developmental manipulations, anatomical and cell biological analyses of reproduction-related changes, and behavioral observation. By virtue of its topic this study will contribute to understanding both sex differences in the brain and the neural basis of maternal as well as paternal behavior. The last contribution will be new to the field since virtually nothing is known about neural structures underlying paternal behavior. Research Career Development support is requested to free the PI form teaching and administrative duties. This will allow him to develop new anatomical, cellular, and molecular strategies to assess the contributions of the sexually dimorphic vasopressin projections to parental behavior.